1. Field of the Invention
The present invention generally relates to an automatic Gamma correction system for displays, and more particularly, to an automatic Gamma correction system in which a novel display driving circuitry designed with a digital/analog converter (DAC) and associated circuitry is used to provide a greater degree of freedom for the realization of the correction of Gamma parameters.
2. Description of the Prior Art
Recently, the technique in the field of displays has grown rapidly with the fast development in opto-electronics. However, for a display (a television having a conventional picture tube or a state-of-the-art thin film transistor-liquid crystal display), the realization of the correction of Gamma parameters has become a key technique. It is mainly due to the fact that the relation between the gray-scale value and the signal voltage as well as the relation between the gray-scale value and the luminance of a display is non-linear, and such non-linearity must be corrected by using Gamma parameters so that the signal voltage and the gray-scale value or the luminance can meet the requirement of linearity and thus high image quality can be obtained. Accordingly, the correction of Gamma parameters is one of the major considerations in the development of display industry. However, due to the inevitable process unreliability, the characteristics of each display are somewhat different, therefore, the individual correction of Gamma parameters of each display is required. It suffers from waste of time and high manufacturing cost.
In the prior arts, in order to achieve automatic correction of Gamma parameters, it has been provided a feedback system with a sensor disposed inside the display, as shown in FIG. 1. Such knowledge is disclosed, for example, in the U.S. Pat. No. 6,046,719 as entitled xe2x80x9cColumn Driver With Switched-Capacitor D/A Converterxe2x80x9d filed on Jul. 7, 1997. As shown in the drawing, a temperature sensor (1014) is disposed in the liquid-crystal display (1012). The lifetime of the display is taken into consideration so as to calculate the Gamma parameters and perform Gamma correction (1010). Later, the result is further input into the column driver (i.e., the data driver) (1018) display. Therefore, the signal voltage is fixed.
However, such a conventional technique, as shown in FIG. 1, has two major setbacks: (1) lack of flexibility in practical use due to the influence of the change in individual display setting upon the correction of Gamma parameters; and (2) incompatibility to different displays when the built-in voltage dividing function of any two Gamma reference voltages is fixed.
Another conventional circuit configuration, as shown in FIG. 2, is provided to improve the control system for the uniformity in luminance and/or color of the display. Such knowledge is disclosed, for example, in the U.S. Pat. No. 6,043,797 as entitled xe2x80x9cColor and Luminance Control System for Liquid Crystal Projection Displayxe2x80x9d filed on Nov. 5, 1996. As shown in the drawing, the display is divided into nine sections (12Axcx9c12N) and their corresponding control units perform the correction of Gamma parameters respectively. The detailed circuits of the embodiments of such a disclosure are shown in FIGS. 3A, 3B and 3C, illustrating the input analog and/or digital RGB signals and the controlling approaches of display driving.
However, such a conventional technique, as shown in FIGS. 2 and 3, has two major setbacks: (1) lack of flexibility in practical use due to the large amount of data storage and complicated Gamma curve calculation for all the possible Gamma correction curves necessary for each display to be stored in the look-up table 100; and (2) sacrificed gray-scale quality due to the changing approach of the gray-scale of image for Garmna correction in digital systems.
Furthermore, the gray-scale values with respect to the external Gamma reference voltages of the data driver used in the mentioned conventional techniques are fixed. Please refer to FIGS. 4A and 4B, wherein FIG. 4A shows the relation curve of the gray-scale values and the voltages and FIG. 4B shows the adjustable voltage range with respect to different gray-scale values. To be more specific, as shown in FIG. 4B, the Gamma reference voltages (V1xcx9cV5) are adjustable with the corresponding gray-scale values (0, 32, 192, 230, and 255) fixed. This reduces the degree of freedom for the realization of the correction of Gamma parameters and leads to greater difference of the transfer curve and the destination function. As a result, the image quality of the display is adversely affected. In other words, sacrificed gray-scale quality is bound to occur when the gray-scale value is changed for Gamma parameter correction.
It is thus the primary object of the present invention to provide an automatic Gamma parameter correction system in which a novel data driver is designed with a digital/analog converter (DAC), wherein the Gamma reference voltage as well as the corresponding gray-scale value is adjustable.
In order to achieve the foregoing object, the present invention provides two methods for gray-scale-to-voltage transfer. For an N-bit system, the first gray-scale-to-voltage transfer method results in 2N divided voltages output into a working display, and the second gray-scale-to-voltage transfer method results in at least 2N divided voltages, among which only 2N divided voltages are corresponded to be output into a series of output buffers. Therefore, according to the present invention, a greater degree of freedom for the realization of the correction of Gamma parameters is obtained, so as to fit the curve representing the transfer function of the destination gray-scale values and the voltages required to drive the working displays properly.
In one embodiment according to the present invention, an automatic Gamma parameter correction system for displays comprises: a plurality of sensors, disposed inside the display or outside the display for obtaining the voltage-to-luminance curve so as to evaluate a set of Gamma reference voltages; a main controller, connected to the sensors to serve as a main control circuit for the system, and further including a central process unit (CPU) and a memory for parameter calculation and data storage. The sensors can be light sensors, temperature sensors, pixel voltage sensors, or a pixel charging/discharging current sensors used for measuring at least one parameter so as to evaluate the voltage-to-luminance curve or the Gamma voltages as well as the corresponding digital gray-scale values required to establish a gray-scale-to-voltage destination curve for driving displays.
The main controller is connected to a programmable Gamma voltage generating means that generates a set of Gamma reference voltages output into the input terminals of a set of programmable switches according to the Gamma reference voltages evaluated by the central process unit in the main controller. The programmable switches are connected to the programmable Gamma voltage generating means so as to receive the output voltages and also connected to a switch control unit. The switch control unit is to interconnect the programmable switches and the voltage dividing circuit with a set of corresponding gray-scale values according to the gray-scale signals with respect to the switch control unit. Furthermore, such a system can be used together with adjusting means for luminance, contrast, and color temperature and a back-lighting control unit.
The input terminal of the switch control unit is connected to the main controller and the output terminals of the switch control unit are connected to the programmable switches, so that the switch control unit interconnects the output terminals of the programmable switches and the voltage dividing circuit having a series divided voltage points and then applies the Gamma reference voltages to the corresponding divided voltage points according to the corresponding gray-scale signals delivered from the central process unit. The output terminals of the programmable switches are connected to the voltage dividing circuit implemented by using a digital-to-analog converter (DAC). For an N-gray-scale system, a voltage dividing circuit can output at least 2N divided voltages, and then the voltages are further connected to a series of output buffers.
When the Gamma parameter correction is performed, the parameters related to the system are determined. The voltage-to-luminance curve of the display is then evaluated by using the sensors according to the driving voltage range determined by the parameters. Later, the main controller determines the destination function of the gray-scale-to-voltage transfer curve, and the voltage dividing circuit further implements the transfer curve. Then, the Gamma reference voltages required by the voltage dividing circuit as well as the corresponding gray-scale values are evaluated. The Gamma reference voltages and the corresponding gray-scale values are interconnected by the programmable switches and the switch control unit, so as to build up a gray-scale-to-voltage curve under the state that the Gamma reference voltages and the corresponding gray-scale values are adjustable. The voltage dividing circuit outputs corresponding voltages to the output buffers according to the input gray-scale values of the image.
From the above description, the present invention provides an automatic Gamma parameter correction method for displays, comprising the steps of: (a) determining related parameters for the displays; (b) determining a driving voltage range according to the parameters; (c) repeating (a) if the determined parameters exceed the driving voltage range for the displays; (d) measuring a voltage-to-luminance curve of the displays; (e) determining a destination function of gray-scale-to-voltage transfer curve; (f) evaluating a set of Gamma reference voltages required by the voltage dividing circuit as well as corresponding gray-scale values; (g) interconnecting the Gamma reference voltages and the corresponding gray-scale values by using the programmable switches and the switch control unit, so as to build up a gray-scale-to-voltage curve; and (h) outputting corresponding voltages to a series of output buffers by using the voltage dividing circuit according to the input gray-scale values of the image.
On the other hand, the present invention provides an automatic Gamma parameter correction method for displays, so as to cooperate with conventional data drivers. The system comprises: a plurality of sensors, disposed inside the display for sensing the relative luminance of a series of voltage signals so as to obtain the voltage-to-luminance curve; a main controller, connected to the sensors to serve as a main control circuit for the system, and further including a central process unit and a memory for parameter calculation and data storage; a programmable Gamma voltage generating means, connected to the main controller and generating a set of Gamma reference voltages output into the input terminal of the data driver according to the reference voltage evaluated by the central process unit in the main controller; and at least a data driver, directly connected to the programmable Gamma voltage generating means and generating a image driving signal delivered into the display according to the Gamma reference voltage outputs by the programmable Gamma voltage generating means. Furthermore, such a system can be used together with adjusting means for luminance, contrast, and color temperature and a back-lighting control unit.
It is preferable that the voltage-to-luminance curve, according to the present invention, can be obtained by evaluating, measuring or table-checking.